1. Field of the Invention
The present invention relates to a pressing device which maintains the raceways of the main moving components of a variable volumetric ratio engine permanently in contact with one another and with the faces on which they bear in the cylinder block.
2. Description of the Related Art
International patents WO98/51911, WO00/31377, WO03/008783, belonging to the Applicant, disclose various mechanical devices for a variable volumetric ratio engine.
It will be seen that international patent WO98/51911, in the name of the Applicant, describes a device which serves to improve the overall efficiency of internal combustion piston engines used at variable load and speed by adapting their effective displacement and/or their volumetric ratio during operation.
It will be observed from international patents WO00/31377 and WO03/008783, in the name of the Applicant, that the mechanical transmission device for a variable volumetric ratio engine comprises at least one cylinder in which there moves a piston which is secured, in its lower portion, to a transmission member cooperating, on the one hand, by means of one small-sized rack, with a rolling guide device and, on the other hand, by means of another large-sized rack, with a toothed wheel secured to a connecting rod, this making it possible to transmit the movement between said piston and said connecting rod.
Said mechanical transmission device for a variable volumetric ratio engine also comprises at least one control rack cooperating with the toothed wheel, means for fastening the piston to the transmission member that offer a clamping preload, connection means which make it possible to stiffen the teeth of the racks, and means for reinforcing and lightening the structure of the toothed wheel.
It will be noted that the minimum operating clearance between the toothings of the large-sized racks and those of the toothed wheel is fixed by the location of raceways formed on said large-sized racks and on said toothed wheel.
It will also be noted that the maximum operating clearance between the toothings of the large-sized racks and those of the toothed wheel is fixed by the difference between, on the one hand, the sum of the dimensions along a horizontal axis of the various moving components of the variable volumetric ratio engine, namely a synchronized roller forming part of the rolling guide device, the toothed wheel, the transmission member secured to the piston, and the control rack, and, on the other hand, the distance between the internal surfaces of the cylinder block on which, on one side of the engine, the synchronized roller and, on the other side of the engine, the control rack come to bear.
The maximum operating clearance between the toothings of the large-sized racks and the toothings of the toothed wheel can be adjusted in various ways which all have the disadvantage of requiring a high degree of precision in the production of the cylinder block and/or of adjustment shims.
This high degree of precision is required to obtain the smallest possible maximum operating clearance between the various raceways of the moving components of the engine so as to obtain the smallest possible maximum operating clearance between the toothings of the large-sized racks and those of the toothed wheel. Obtaining said smallest possible maximum operating clearance is necessary to limit the acoustic emissions of the engine which result particularly from the clearance between the teeth of the toothed wheel and the teeth of the racks with which said toothed wheel cooperates, the later clearance giving rise to hammering.
Equally, a high degree of precision is required for the production of the cylinder block and/or the adjustment shims in order to limit as far as possible the defects in parallelism between the various internal functional surfaces of said cylinder block. This is because said parallelism defects can lead to the moving components jamming inside said cylinder block when the engine is operating.
In addition to providing a high degree of precision for the cylinder block and/or the adjustment shims in order to limit the acoustic emissions of the engine and prevent any jamming of the moving components, it should also be ensured that the differences in temperature existing between said cylinder block and the moving components of the engine do not lead either to excessive clearances which can increase the acoustic emissions or to zero or negative clearances which can destroy the engine.
Specifically, the differences in temperature can lead to an expansion of the moving components which differs from that of the cylinder block, and hence to negative or positive variations in the operating clearance of the engine.
High temperature differences can also occur in operation between the top and bottom parts of the cylinder block. These differences can modify the orientation of the surface secured to the cylinder block along which the synchronized roller rolls.
Consequently, the maximum operating clearance between the various raceways of the moving components of the engine can vary during the stroke of the piston.
Another production difficulty stems from the need to reduce as far as possible the operating clearance between the jack piston which actuates the control rack and its bore in order to limit the acoustic emissions of the engine. This is because the jack piston comes to bear cyclically on either side of its bore because of the tilting of the rack which takes place under the thrust action of the toothings alternately above and below the bearing point of said control rack on the cylinder block, said bearing point being embodied for example by a ball joint connection as described in international patent application PCT/FR05/00584 belonging to the applicant.
Moreover, another defect relating to the operation of the control rack by the control jack will be noted: said operation takes place less quickly to increase the volumetric ratio than to lower it. This is due to the fact that the volumetric ratio is reduced by using the high forces applied to the control jack by the expansion of the gases, while the volumetric ratio is increased by using the less intense forces generated by the inertia of those parts of the engine subjected to a reciprocating movement.